Effect of inclination angle of lower tube on saturated pool boiling heat transfer of upper tube

An experimental study was conducted to examine the effects of the inclination angle and heat flux of the tube located at the bottom of the vertically arranged tube bundle on the pool boiling heat transfer of the upper tube. In the experiment, two stainless steel tubes submerged in saturated water at atmospheric pressure were used. The angle of inclination varied from 0 degrees to 90 degrees at 15 degrees intervals. When the inclination angle of the lower tube is increased, the length of the lower tube projected onto the upper tube decreases, and thus the heat transfer coefficient tends to decrease. However, when the angle of the lower tube is between 45 degrees to 75 degrees, bubbles gather in the narrow area, resulting in a strong flow, which tends to increase the heat transfer coefficient. When the heat flux of the lower tube was high and the heat flux of the upper tube was low, an increase in the heat transfer coefficient of the upper tube was clearly observed.